A new study finds that when healthy adults combine an eight-hour eating window with regular exercise, they lose more fat—without sacrificing lean muscle—compared to exercise alone.
“We saw that this did lead to more fat loss and reduced body fat percentage over time when healthy adults were following both exercise with time-restricting eating compared to those who were only exercising for at least four weeks,” said study co-author Nadeeja Wijayatunga.
Wijayatunga and Michael Hays, study lead author, began their study after seeing the dramatic rise in time-restricted eating. They conducted a systematic review and meta-analysis where they analyzed data from 15 studies conducted on time-restricted eating with exercise from the last decade. Time-restricted eating is one of many diets included in the umbrella term intermittent fasting.
“People like time-restricted eating because they feel it’s easier to adhere to because they don’t have to think too much,” Wijayatunga said. “It’s all about time, not calorie-counting or watching out for certain foods.”
Intermittent fasting has quickly become one of the most popular diets in the U.S., with 12 percent of Americans having tried it, according to the 2023 International Food and Health Survey. The science surrounding time-restricted eating, however, is still developing, according to Hays “For some people, this may be a good technique to help with body composition goals,” he said. “It’s just another tool, but more studies need to come out to really understand how this works in humans.”
While the difference between those who exercised while following a time-restricted diet and those who used exercise alone was slight, the two groups in the studies were already very healthy individuals. “In most cases, these were healthy adults,” Hays said. “They were already physically fit and already had exercise routines. When you already have athletic, lean people and you decrease their body fat percentage, that’s significant.”
Time-restricted eating has been criticized for possibly leading to a loss of lean mass—all the muscles, organs and other tissues that make up the human body. In their study, Hays and Wijayatunga found that when paired with exercise, time-restricted eating did not lead to a reduction in lean mass, even for those who lost body fat.
“That’s why you want to couple diet with exercise,” Hays emphasized. “When you’re losing weight, you never want to lose lean tissue. You want to lose fat.”
Reference
1. Harry M. Hays, Pouria Sefidmooye Azar, Minsoo Kang, Grant M. Tinsley, Nadeeja N. Wijayatunga. Effects of time-restricted eating with exercise on body composition in adults: a systematic review and meta-analysis. International Journal of Obesity, 2025; DOI: 10.1038/s41366-024-01704-2.
